In the production process of light-sensitive silver halide photographic materials (hereinafter also "light-sensitive material"), silver halide photographic emulsions having been subjected to chemical ripening are often stored for a certain time in a given environment before they are coated. On that occasion, ripening may proceed because of the presence of a spectral sensitizing dye having not reacted with silver halide grains and remaining in a very small quantity, sometimes resulting in an increase in fog of emulsions after they have been coated and dried or a change in sensitivity when the spectral sensitizing dye adsorbed on silver halide grains become released therefrom during storage.
In recent years, there is also an increasing demand for making light-sensitive materials higher in sensitivity, and means for improving both light absorption characteristics and developability of silver halide have been hitherto taken as means for achieving high sensitivity. For example, for the purpose of improving spectral sensitivity, Japanese Patent Publications Open to Public Inspection [hereinafter referred to as Japanese Patent O.P.I. Publication(s)] No. 51627/1963 and No. 77443/1984 disclose a method in which a water-soluble iodide is added to a silver iodobromide emulsion.
This method can be effective for increasing adsorbability of spectral sensitizing dyes on the surfaces of silver halide grains to adjust spectral sensitivity distribution or decrease the release of spectral sensitizing dyes in an environment of high humidity and high temperature, but has e disadvantage of causing a lowering of sensitivity when the water-soluble iodide is added to such an extent that the adsorbability of spectral sensitizing dyes is well increased. In addition, in this method, the resulting emulsions often undergo changes in sensitivity with time probably because the reaction of adsorption of iodide ions on the surfaces of silver halide grains is so rapid that the adsorption reaction is non-uniform and unstable.
Meanwhile, as a means for increasing sensitivity of silver chlorobromide emulsions and improving their aging stability, a method in which a water-soluble bromide or a water-soluble iodide is added is known in the art (Japanese Patent O.P.I. Publications No. 96331/982 and No. 5238/1984).
This method, however, requires adding the water-soluble bromide in an amount of 5 to 50 mol when it is added alone, and has also a disadvantage of causing an increase of ill influence (e.g., a lowering of sensitivity or a contrast reduction) due to flow-out of bromide ions to a processing solution during developing. In a method in which a water-soluble bromide and a water-soluble iodide are used in combination, very remarkable changes in photographic performance (e.g., a lowering of sensitivity, a contrast reduction and an increase in fog) may occur in the course of preparation of emulsions up to their coating, probably because of the non-uniformity or unstableness of the adsorption reaction of iodide ions.
Thus, conventional means for solving the problems of a lowering of spectral sensitivity and a deterioration of aging stability that may arise as silver halides composed in variety are made higher in sensitivity have been very unsatisfactory.